Combustion engines such as diesel engines, gasoline engines, and gaseous-fuel-powered engines burn a mixture of air and fuel within the engine, generating mechanical power and a consequent flow of exhaust. Engine exhaust contains, among other things, unburnt fuel, particulate matter such as soot, and harmful gases such as nitrous oxide or carbon monoxide. Modern engines must meet stringent emissions standards, which permit engines to discharge only miniscule levels of nitrous oxide and soot into the atmosphere. To comply with these standards, an engine design must, therefore, balance the desire for increased power output with the need to reduce harmful emissions.
Modern engines often include a turbocharger, which helps to increase the power output by forcing more air into the combustion chambers of the engine than otherwise possible. The increased air intake permits the combustion of more fuel in the combustion chambers, increasing the power generated by the engine. To reduce harmful emissions, modern engines often use an exhaust gas recirculation (EGR) system, which recirculates a portion of the exhaust through the combustion chambers to reduce the amount of harmful emissions released into the atmosphere by the engine. Diverting some of the exhaust to the EGR system, however, decreases the amount of exhaust available to propel the turbocharger, which may decrease the power output from the engine.
One attempt to address the problems described above is disclosed in U.S. Pat. No. 5,517,976 of Bächle et al. that issued on May 21, 1996 (“the '976 patent”). The '976 patent discloses a diesel engine having two groups of cylinders. Exhaust from the first group of cylinders propels a turbocharger before being discharged to the atmosphere. An exhaust gas return device returns exhaust gas from the second group of cylinders to a fresh air supply for all engine cylinders or only the first group of cylinders. The '976 patent further discloses a connector conduit between the exhaust gas discharge from the first group of cylinders and the exhaust gas return from the second group of cylinders. The connector conduit includes a device for adjusting the cross-sectional flow area in the conduit to control the rate of return of exhaust gas in the exhaust gas return device. The system of the '976 patent also includes a soot filter located within the exhaust gas return device.
Although the system of the '976 patent may help to lower engine emissions, by recirculating the exhaust generated by the second group of cylinders through all cylinders of the engine, the system may still be less than optimal. Specifically, the system of the '976 patent controls the rate of exhaust gas flow in the exhaust gas return device using a single variable flow area device in the connector conduit. As a result, the system of the '976 patent may not be able to deliver sufficient exhaust to propel the turbocharger while simultaneously recirculating sufficient amount of exhaust through the engine to meet today's stringent emissions standards. Moreover, the soot filter in the exhaust gas return device of the '976 system may have to be periodically removed for cleaning, which may affect the availability of the engine and may increase the cost of operating the engine.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.